Testing Pendant Chains Dynamic in Model PDMS Networks by NOE Measurements

F. CAMPISE; R.H. ACOSTA; M.A VILLAR; E.M. VALLÉS; D.A. VEGA; G.A. MONTI

Aveiro

Congreso; IV Ibero-American NMR Meeting, VI Reunión Bienal del GERMN, III Iberian NMR Meeting; 2012

Universidad de Aveiro

Over the last 5 decades the dynamic response of entangled polymer melts has been an outstanding problem in polymer science. Most of the viscoelastic and diffusive properties of polymer melts and concentrated polymer solutions are profoundly influenced by topological interactions. The most successful model to deal with topological constrains is the tube model. According to this model, the topological confinement exerted on a given molecule by the surrounding media can be modeled as an hypothetical tube that severely suppress the motion perpendicular to the tube?s local axis, but permits the diffusion along the tube. Polydimethylsiloxane (PDMS) networks are ideal systems to probe chain dynamics. In PDMS networks entangled and dangling chains have the same chemical structure. This means that the whole sample has the same spectroscopic components. In this work, in an attempt to probe pendant chains dynamic, we applied a pulse sequence that uses the differences between proton transverse relaxation times to generate a magnetization gradient and also to determine the magnetization transfer via Nuclear Overhauser Effect (NOE. Experiments were conducted on tri and tetra-functional networks with pendant chains of different molecular weight. For selected tri and tetra-functional networks, experiments as a function of the temperature were carried out. In these cases NOE magnetization transfer responds to an Arrhenius process, enabling the determination of activation energies.